This invention relates to incandescent lamps in which a filament of wire such as tungsten is heated to incandescence by electric current. Typically, such lamps have a filament, which is a generally continuous coil from end to end, disposed in an envelope such as glass in some form of continuous cavity around the filament.
For certain applications, a problem with such sources has been the inability to construct a linear coil to operate at a high color temperature with a relatively low power. High color temperature sources, 2800.degree. - 3100.degree.K, are required for acceptable efficiencies when used with visible responding systems, i.e. systems wherein there is a desired response to visible light as for example in a photocopying environment. To operate at these temperatures requires the use of a halogen cycle to prevent tube blackening and, in conventional lamps the lower limit of power required to maintain a functioning halogen cycle is approximately 150 watts per inch.
It is desired, and an object of this invention, to provide such a lamp which is operative at power levels on the order of 10 to 20 watts per inch. Ordinarily with this little power dissipated within the lamp, the temperature would not be sufficient to maintain the require halogen cycle.